In the, IIRC, early 1980s, I invented a better device than this and tested a prototype in hot, humid Florida in summer. It worked.
Imagine a long, skinny Camelbak that's about 3 0" long and insulated on three sides filled with ice that you wear around your neck like a horse collar. At the neck, it velcros to hold it closer to the carotid artery to cool the blood as it goes to the brain.
As the ice melts, you could drink the ice water from a tube (like with a Camelbak) for an additional cooling effect.
The first prototype worked great for about 45 minutes until the ice melted. With better insulation, it might have lasted over an hour.
I even considered trying to patent it, but I thought cooling the blood going to the brain might trick the body somehow and wind up killing people so I dropped the idea.